1. Field of the Invention:
The present invention relates to an electronic endoscope system in which a solid-state imaging device is used as an imaging means and incorporated in an insertional part.
2. Description of the Related Art:
In recent years, an endoscope, of which elongated insertional part is inserted in a body cavity in order to observe an organ, or if necessary, of which therapeutic instrument channel is used to insert a therapeutic instrument for undertaking various kinds of therapy and treatment, has been adopted widely.
This kind of endoscope includes an electronic endoscope in which a solid-state imaging device such as a charge coupled device (hereinafter CCD) is used as an imaging means.
In the electronic endoscope, an optical image of an object is formed on an imaging surface of a solid-state imaging device via an objective optical system, the optical image formed on the imaging surface is converted into an electric signal, and then the electric signal resulting from photoelectric conversion is transmitted to a signal processing means by way of an electric signal transmitting means.
The signal processing means transforms the electric signal into a video signal. The video signal is then transmitted to a monitor unit, whereby the optical image of the object is displayed on a screen of the monitor unit for the purpose of observation.
When the electronic endoscope is used in combination with an external unit, for example, an electric equipment such as a high-frequency therapeutic instrument, a high-frequency noise radiating from the high-frequency therapeutic instrument is liable to mix with an electric signal that results from photoelectric conversion performed by the solid-state imaging device and is transmitted to the signal processing means. When the high-frequency noise mixes with an electric signal being transmitted to the signal processing means, the quality of an endoscopic image appearing on a screen of the monitor unit deteriorates markedly.
In an effort to prevent a noise from mixing with an electric signal, which results from photoelectric conversion performed by a solid-state imaging device, due to the use of an electric equipment in combination with an electronic endoscope having the solid-state imaging device, a conducting member is used as an armor of an insertional part of an endoscope. The conducting member is grounded via a ground in a signal processing means and thus shielded. Moreover, an isolation means is used to isolate the signal processing means from an external power supply means for supplying power to the signal processing means.
However, if the isolation between the signal processing means and external power supply means should become defective, there is a possibility that the conducting member serving as the armor of the insertional part of the electronic endoscope may conduct electricity to a ground in the power supply means. In the state in which the conducting member of the insertional part is conducting electricity to the ground, if a high-frequency therapeutic instrument is used, high-frequency current flows from the high-frequency therapeutic instrument to the conducting member serving as the armor of the insertional part of the electronic endoscope and realizing a shield. This causes high-frequency current to flow from the ground in the signal processing means toward the ground in the power supply means. At this time, if the conducting member serving as the armor of the insertional part is situated inside a body cavity, an unexpected burn may occur at a position in the body cavity near the conducting member.
In an electronic endoscope, a printed-circuit board on which an IC and other circuit elements are mounted and which realizes a signal processor is situated in the vicinity of a solid-state imaging device in order to process a signal acquired by the solid-state imaging device. For improving an signal-to-noise ratio, the printed-circuit board should be located near the solid-state imaging device. However, when an attempt is made to install both the solid-state imaging device and printed-circuit board in a distal portion of the endoscope, the distal portion must be made longer. This degrades the smoothness in inserting the endoscope into a body cavity.
Japanese Patent Laid-Open No. 61-250608 has disclosed an art in which a solid-state imaging device is incorporated in a first rigid unit in a distal portion of an insertional part, and a signal processor is incorporated in a second rigid unit situated in a proximal portion of the insertional part away from the first rigid unit.
In the signal processor disclosed in the unexamined publication, as shown in FIG. 1, center conductors 302 of signal cables 301 that are coaxial cables are attached to terminals 304 formed on a signal processor printed-circuit board 303 by performing soldering or the like. Outer conductors (shielded cables) 306 of the signal cables 301 are immobilized all together using a copper wire 307 and soldered to a conductive holder 305 to which the signal processor printed-circuit board 303 is fixed closely. Thus, the potentials at all the outer conductors 306 and holder 305 are equalized. This helps further stabilize shielding.
The terminals 304 are printed on the front side of the printed-circuit board 303, and extending to the end of the printed-circuit board for reasons of processing. The terminals 304 and outer conductors 306 may approach too closely each other at a junction 308 between the holder 305 and printed-circuit board 303 and then conduct electricity. If the terminals 304 and outer conductors 306 should conduct electricity, not only imaging is disabled but also a solid-state imaging device or signal processor is destroyed.
When an attempt is made to locate all the terminals 304 at substantially the same position, signal lines for inputting or outputting a video signal must be laid out over a longer distance. Electric noises originating from other terminals including a power supply terminal and other signal lines are liable to mix with a video signal. This results in deteriorated image quality.
When a solid-state imaging device and signal processor are separated from each other and linked by signal lines, the signal lines may distribute noises or may be susceptible to external noises. In the aforesaid structure, it is therefore requested to shorten the length of a distal rigid unit and improve shielding capability.
The solid-state imaging device incorporated in the first rigid unit is linked to the signal processor incorporated in the second rigid unit by signal lines that are routed through, for example, a bending section communicating the first rigid unit with the second rigid unit. When the bending section is angled, pulling force or compressing force works on the signal lines. This may cause a disconnection at a junction between the signal lines and solid-state imaging device or between the signal lines and signal processor.
Some of signals transferred between the solid-state imaging device and signal processing means are transmitted via the signal processor, while the others thereof are transmitted directly. In the structure in which the solid-state imaging device and signal processor are separated from each other, no consideration is taken into the signal lines directly linking the imaging device and signal processing means.
In an electronic endoscope, generally, not only an imaging unit but also a therapeutic instrument channel through which a light guide for transmitting illumination light or a therapeutic instrument is routed, and an aeration/affusion channel are formed in a distal portion. Japanese Unexamined Utility Model Publication No. 60-9041 has disclosed an art in which a light guide is installed so that the light guide can lie along the circumference of an imaging unit situated in a distal portion of an electronic endoscope. This structure contributes to an increase in amount of illumination light.
When the art disclosed in the utility model publication is adapted to an electronic endoscope, any of wires constituting the light guide may be broken. This results in a decreased amount of emitted light. In an effort to prevent the decrease in amount of emitted light, the light guide wires to be routed along the circumference of the imaging unit and extended toward the optimal portion of the endoscope are sheathed with a silicon tube or the like and thus bundled at the back end of the imaging unit in the distal portion of the endoscope distal to the bending section.
However, as shown in FIG. 2, when a light guide 313 lying along the circumference of an imaging unit 312 incorporated in a distal structure 311 of an endoscope 310 is extended toward the proximal portion of the endoscope, the portion of the endoscope sheathed with a silicon tube 317 is sandwiched between a junction 315, at which the distal structure 311 is joined with the distal end of a bending section 314, and a signal cable 316 extending from the imaging unit 312 because of a narrow space A between the junction 315 and the signal cable 316. In this situation, if angling is repeated, any of the wires constituting the light guide located near the silicon tube in the space A may be broken.
For preventing the light guide 313 from being broken in the distal structure, it is essential to widen the space A between the junction 315 and signal cable 316. If the outer diameter of the distal structure 311 is made larger in order to ensure a wide space, it contradicts the concept that the diameter of an insertional part of an endoscope is decreased in an effort to alleviate patient discomfort occurring at the time of inserting the insertional part into a body cavity.